Modifying core WordPress files is a quick way to introduce security vulnerabilities, break your site, and break future updates. From the perspective of a developer, nothing is worse than searching through a theme and plugins for a problem only to discover a previous developer modified a core WordPress file an introduced a bug.
I wrote a simple Node module that lets you easily check WordPress installations for modified or removed core files. Install the detect-wp-core-modifications npm package with the following shell command:
npm install -g detect-wp-core-modifications
You can run the command without any arguments from within the root of a WordPress installation with the following shell
You can also specify a relative or absolute path to a WordPress installation: